Poly(Meth-)Acrylic Resin-based coating agent which can be cross-lined with Isocyanate

ABSTRACT

The present invention provides a coating composition and a process for producing a multicoat finish therefrom. The coating composition has a binder component obtained by polymerizing: (a) from 10 to 51% by weight of a mixture of hydroxy n-butyl (meth)acrylate(s) and hydroxy n-propyl (meth)acrylate(s), (b) from 0 to 20% by weight of at least one further hydroxyl group-containing monomer, (c) from 28 to 85% by weight of at least one (cyclo)aliphatic (meth)acrylic acid ester, (d) from 0 to 25% by weight of at least one aromatic vinyl compound, (e) from 0 to 5% by weight of at least one unsaturated carboxylic acid, and (f) from 0 to 20% by weight of further monomers, to give a polyacrylate resin having a hydroxyl number of from 60 to 200, an acid number of from 0 to 35, and an Mn of from 1000 to 5000. The coating composition also has a crosslinking component that is a mixture comprising a polyisocyanate having an average functionality of from 3 to 4 and having a uretdione group content of less than 5%, and optionally a polyisocyanate having an average functionality of from 2 to 3 and having a uretdione group content of from 20 to 40%, and optionally a further polyisocyanate.

FIELD OF THE INVENTION

The present invention relates to a coating composition comprising

(A) at least one hydroxyl group-containing poly-acrylate resin, and

(B) at least one crosslinking agent.

The present invention also relates to processes for producing amulticoat protective and/or decorative finish on a substrate surface andto the use of the coating compositions in the sector of automotiverefinishing.

BACKGROUND AND SUMMARY OF THE INVENTION

Multilayer coatings, especially two-coat metallic finishes, are producedin particular by the basecoat/clearcoat method. This method is known andis described, for example, in U.S. Pat. No. 3,639,147 and EP-A-38 127.

The basecoat/clearcoat method can be used to produce finishes whosesuperiority over one-coat finishes is manifested in an enhanced effectand in the possibility of producing finishes with more brilliant andmore clean colors.

The basecoat which is applied first of all determines, depending on thenature, quantity and spatial orientation of the pigments employed, thecolor and, if appropriate, the effect (e.g. metallic effect or pearlluster effect) of the finish.

Following application of the basecoat, at least some of the organicsolvents and/or at least some of the water are or is removed from theapplied basecoat film in an evaporation phase. A nonaqueous, transparenttopcoat is then applied to this predried basecoat (wet-on-wet method).Basecoat and topcoat are then dried together.

The applied transparent topcoat gives the two-coat finish gloss andfullness and protects the pigmented coat applied from chemical andphysical attack.

Using the method under discussion, it is only possible to obtainhigh-quality two-coat finishes if the transparent topcoat applied doesnot adversely affect the applied basecoat in such a way that the opticaleffect is impaired (e.g. clouding). On the other hand, the transparenttopcoat must have a composition which ensures that it adheres well tothe basecoat after the drying process. Further important propertieswhich the transparent topcoat obtained after the drying process isrequired to have are a high degree of transparency, very good topcoatappearance, good gloss and good mechanical properties such as hardness,mar resistance and elasticity. Not least among the requirements, thetransparent topcoat obtained after the drying process must have a highresistance to climatic effects (e.g. fluctuations in temperature,moisture in the form of water vapor, rain and dew, radiation-inducedstress, etc.) and to attacks by acids or other chemicals such as, forexample, organic solvents.

JP-A-1-158079 describes nonaqueous transparent topcoats for two-coatfinishes of the basecoat/clearcoat type, which contain a hydroxylgroup-containing polyacrylate resin which is obtainable by polymerizingfrom 10 to 50% by weight of an adduct of a cyclic ester, for exampleε-caprolactone with hydroxyethyl acrylate or methacrylate, from 0 to 40%by weight of a hydroxyalkyl acrylate or methacrylate and from 30 to 80%by weight of a copolymerizable vinyl monomer to give a polyacrylateresin having a hydroxyl number of from 60 to 160, an acid number of from0 to 40 and a glass transition temperature of from -50 to +40° C. Thetransparent topcoats described in JP-A-1-158079 give finishes which arein need of improvement, especially with respect to their acid resistanceand adhesion.

JP-A-4-1254 discloses coating compositions which contain, in addition toa crosslinking agent, a hydroxyl group-containing polyacrylate resinwhich has been prepared using 4-t-butylcyclohexyl acrylate and/or4-t-butylcyclohexyl methacrylate as monomer component. The hydroxylgroup-containing monomer employed for the preparation of thepolyacrylate resin comprises, in particular, hydroxyethyl acrylate andhydroxyethyl methacrylate. These coating compositions known fromJP-A-4-1254 have the particular disadvantage, when used as a transparenttopcoat over a basecoat, that the resulting coatings are of inadequateadhesion to the basecoat. Furthermore, the resulting coatings have apoor solvent resistance, a high swellability and a poor overcoatability.

Finally, German Patent Application P 43 10 414.2, which is not a priorpublication, describes coating compositions of the type describedinitially which contain as binder a hydroxyl group-containingpolyacrylate resin which has been prepared using 4-hydroxy-n-butylacrylate and/or 4-hyroxy-n-butyl methacrylate as monomer component. Thecoating compositions described therein are employed in particular in thesector of automotive production-line finishing. Coating compositions forthe sector of automotive refinishing are not described in thisapplication.

The object of the present invention was therefore to provide coatingcompositions which, when used as transparent topcoat over a basecoat,lead to coatings whose mar resistance is improved relative to knowncoating compositions. In addition, the resulting coatings should have inparticular a good adhesion to the basecoat and, furthermore, a highdegree of hardness coupled with good elasticity, a very good topcoatappearance, a high degree of transparency and good gloss. In addition,the resulting coatings should possess good polishability and goodweathering resistance. Finally, the coating compositions should bereadily processable and should be suitable for automotive refinishing;that is, they should be able to cure fully at low temperatures of ingeneral below 120° C., preferably below 80° C. Even at these lowtemperatures the coating compositions should reach full cure rapidly (inparticular, should display rapid through-drying) while neverthelessremaining processable (pot life) for as long as possible.

Surprisingly, this object is achieved by a coating composition of thetype described initially, which is characterized in that

1.) component (A) is a hydroxyl group-containing polyacrylate resinwhich is obtainable by polymerizing

(a) from 10 to 51% by weight of a mixture comprising

(a1) one or more monomers selected from the group consisting of4-hydroxy-n-butyl acrylate and/or 4-hyroxy-n-butyl methacrylate and/or3-hydroxy-n-butyl acrylate and/or 3-hydroxy-n-butyl methacrylate, and

(a2) one or more monomers selected from the group consisting of3-hydroxy-n-propyl acrylate and/or 3-hydroxy-n-propyl methacrylateand/or 2-hydroxy-n-propyl acrylate and/or 2-hydroxy-n-propylmethacrylate,

(b) from 0 to 20% by weight of a hydroxyl group-containing ester ofacrylic acid or of methacrylic acid which is different from (a) and hasat least 5 carbon atoms in the alcohol residue and/or of a hydroxylgroup-containing ester of a polymerizable ethylenically unsaturatedcarboxylic acid, which is different from (a), or of a mixture of suchmonomers,

(c) from 28 to 85% by weight of an aliphatic or cycloaliphatic ester ofacrylic acid or of methacrylic acid which is different from (a) and (b)and has at least 4 carbon atoms in the alcohol residue, or of a mixtureof such monomers,

(d) from 0 to 25% by weight of an aromatic vinyl hydrocarbon which isdifferent from (a), (b) and (c), or of a mixture of such monomers,

(e) from 0 to 5% by weight of an ethylenically unsaturated carboxylicacid, or of a mixture of ethylenically unsaturated carboxylic acids, and

(f) from 0 to 20% by weight of an ethylenically unsaturated monomerwhich is different from (a), (b), (c), (d) and (e), or of a mixture ofsuch monomers

to give a polyacrylate resin having a hydroxyl number of from 60 to 200mg of KOH/g, an acid number of from 0 to 35 mg of KOH/g and anumber-average molecular weight of from 1000 to 5000, the sum of theproportions by weight of components (a) to (f) being in each case 100%by weight, and

2.) component (B) is a mixture comprising

(B1) at least one polymer of an aliphatic and/or cycloaliphatic and/orof an araliphatic di- and/or polyisocyanate having an averagefunctionality of from 3 to 4 and having a uretdione group content of notmore than 5%,

(B2) optionally at least one polymer of an aliphatic and/orcycloaliphatic and/or of an araliphatic di- and/or polyisocyanate havingan average functionality of from 2 to 3 and having a uretdione groupcontent of from 20 to 40%, and

(B3) optionally at least one aliphatic and/or cycloaliphatic and/oraraliphatic di- or polyisocyanate which is different from (B1) and (B2).

The present invention also relates to a process for producing amultilayer coating on a substrate surface, using these coatingcompositions, and to the use of the coating compositions in the sectorof automotive refinishing.

It is surprising and was not foreseeable that the coating compositionsaccording to the invention, when used as transparent topcoat over abasecoat, would be notable for very good mar resistance and very goodadhesion to the basecoat. A further advantage is that the coatingcompositions lead to coatings having a high degree of hardness coupledwith good elasticity, very good topcoat appearance, a high degree oftransparency, good gloss, good polishability and high resistance toclimatic effects (such as, for example, fluctuations in temperature,moisture in the form of water vapor, rain and dew, radiation-inducedstress, etc.). Furthermore, the coating compositions have the advantagethat they are readily processable and can be cured fully at lowtemperatures and can therefore be employed in the sector of automotiverefinishing. Even when the coating compositions are cured at lowtemperatures, the coating compositions rapidly reach full cure whilenevertheless remaining processable for a long time (pot life).

DETAILED DESCRIPTION

The text below now describes the individual constituents of the coatingcomposition according to the invention in more detail. The acrylateresin (A) which is employed in accordance with the invention isobtainable by polymerizing

(a) from 10 to 51% by weight, preferably from 10 to 35% by weight, of amixture comprising

(a1) one or more monomers selected from the group consisting of4-hydroxy-n-butyl acrylate and/or 4-hyroxy-n-butyl methacrylate and/or3-hydroxy-n-butyl acrylate and/or 3-hydroxy-n-butyl methacrylate, and

(a2) one or more monomers selected from the group consisting of3-hydroxy-n-propyl acrylate and/or 3-hydroxy-n-propyl methacrylateand/or 2-hydroxy-n-propyl acrylate and/or 2-hydroxy-n-propylmethacrylate,

(b) from 0 to 20% by weight, preferably from 0 to 10% by weight, of ahydroxyl group-containing ester of acrylic acid or of methacrylic acidwhich is different from (a) and has at least 5 carbon atoms in thealcohol residue and/or of a hydroxyl group-containing ester of apolymerizable ethylenically unsaturated carboxylic acid, which isdifferent from (a), or of a mixture of such monomers,

(c) from 28 to 85% by weight, preferably from 40 to 70% by weight, of analiphatic or cycloaliphatic ester of acrylic acid or of methacrylic acidwhich is different from (a) and (b) and has at least 4 carbon atoms inthe alcohol residue, or of a mixture of such monomers,

(d) from 0 to 25% by weight, preferably from 5 to 20% by weight, of anaromatic vinyl hydrocarbon which is different from (a), (b) and (c), orof a mixture of such monomers,

(e) from 0 to 5% by weight, preferably from 1 to 3% by weight, of anethylenically unsaturated carboxylic acid, or of a mixture ofethylenically unsaturated carboxylic acids, and

(f) from 0 to 20% by weight, preferably from 0 to 15% by weight, of anethylenically unsaturated monomer which is different from (a), (b), (c),(d) and (e), or of a mixture of such monomers

to give a polyacrylate resin having a hydroxyl number of from 60 to 200,preferably from 80 to 160, mg of KOH/g, an acid number of from 0 to 35,preferably from 0 to 25, mg of KOH/g and a number-average molecularweight of from 1000 to 5000, preferably from 1800 to 3500, the sum ofthe proportions by weight of components (a) to (f) being in each case100% by weight.

The polyacrylate resins which are employed in accordance with theinvention can be prepared by generally well-known methods ofpolymerization. Polymerization methods for the preparation ofpolyacrylate resins are generally known and are described in numerousreferences (cf. e.g.: Houben-Weyl, Methoden der organischen Chemie[Methods of organic chemistry], 4th edition, volume 14/1, pages 24 to255 (1961)).

The polyacrylate resins which were employed in accordance with theinvention are preferably prepared with the aid of the solutionpolymerization method. In this method, commonly, an organic solvent orsolvent mixture is initially introduced and is heated to boiling. Themonomer mixture to be polymerized, along with one or more polymerizationinitiators, are then added continuously to this organic solvent orsolvent mixture. Polymerization is carried out at temperatures ofbetween 100 and 160° C., preferably between 130 and 150° C. Thepolymerization initiators employed are preferably initiators which formfree radicals. The nature and quantity of the initiator are commonlychosen such that, at the polymerization temperature during the feedphase, the supply of radicals remains as constant as possible.

Examples of initiators which can be employed are: di-tert-butylperoxide, tert-butyl hydroperoxide, tert-butyl peroxybenzoate,tert-butyl peroxypivalate, tert-butyl peroxy-3,5,5-trimethylhexanate,tert-butyl peroxy-2-ethylhexanoate, dicumyl peroxide, cumylhydroperoxide, tert-amyl peroxybenzoate, tert-amylperoxy-2-ethylhexanoate, diacyl peroxides, for example diacetylperoxide, peroxyketals, 2,2-di(tert-amylperoxy)propane, ethyl3,3-di(tert-amylperoxy)butyrate and thermally labile, highly substitutedethane derivatives, for example those based on silyl-substituted ethanederivatives and based on benzopinacol. In addition, aliphatic azocompounds such as, for example, azoisovaleronitrile andazobiscyclohexanenitrile can also be employed. The quantity of initiatoris in most cases from 0.1 to 8% by weight, based on the quantity ofmonomer to be processed, but may also be higher if desired. Theinitiator, dissolved in a portion of the solvent employed for thepolymerization, is metered in gradually during the polymerizationreaction. The initiator feed preferably lasts from about 0.5 to 2 hourslonger than the monomer feed, so as to achieve a good action even duringthe after polymerization phase. If initiators having only a lowdecomposition rate under the prevailing reaction conditions areemployed, then it is also possible to include the initiator in theinitial charge.

The polymerization conditions (reaction temperature, feed time of themonomer mixture, nature and quantity of the organic solvents andpolymerization initiators, possible use of molecular weight regulators,for example mercaptans, thioglycolic esters and hydrogen chlorides) arechosen such that the polyacrylate resins which are employed inaccordance with the invention have a number-average molecular weight offrom 1000 to 5000, preferably from 1800 to 3500 (determined by gelpermeation chromatography using polystyrene as calibrating material).

The acid number of the polyacrylate resins which are employed inaccordance with the invention can be adjusted by the person skilled inthe art by using appropriate quantities of component (e). Similarcomments apply to the adjustment of the hydroxyl number. It can becontrolled by way of the quantity of component (a) and (b) which isemployed.

It is essential to the invention that the mixture employed as component(a) comprises

(a1) one or more monomers selected from the group consisting of4-hydroxy-n-butyl acrylate and/or 4-hydroxy-n-butyl methacrylate and/or3-hydroxy-n-butyl acrylate and/or 3-hydroxy-n-butyl methacrylate, and

(a2) one or more monomers selected from the group consisting of3-hydroxy-n-propyl acrylate and/or 3-hydroxy-n-propyl methacrylateand/or 2-hydroxy-n-propyl acrylate and/or 2-hydroxy-n-propylmethacrylate.

The mixture preferably employed as component (a) comprises

(a1) from 10 to 85% by weight, preferably from 20 to 65% by weight, ofcomponent (a1), and

(a2) from 15 to 90% by weight, preferably from 35 to 80% by weight, ofcomponent (a2),

the sum of the proportions by weight of components (a1) and (a2) beingin each case 100% by weight.

The composition of component (a) is preferably chosen such that theproduct of the polymerization of component (a) alone is a polyacrylateresin having a glass transition temperature of from -62° C. to +65° C.,preferably from -50° C. to +35° C.

The glass transition temperature can be calculated approximately by theperson skilled in the art with the aid of the formula ##EQU1## T_(G)=glass transition temperature of the polymer x=number of differentmonomers incorporated by polymerization

W_(n) =proportion by weight of the nth monomer

T_(Gn) =glass transition temperature of the homopolymer of the nthmonomer.

The mixture which is employed in particular as component a) comprises

(a1) 4-hydroxy-n-butyl acrylate and/or 3-hydroxy-n-butyl acrylate, and

(a2) 3-hydroxy-n-propyl methacrylate and/or 2-hydroxy-n-propylmethacrylate.

As a further hydroxyl group-containing monomer (component (b)) it ispossible if desired, for the preparation of the acrylate resin, toemploy further hydroxyl group-containing esters of acrylic acid and/ormethacrylic acid, in which the alcohol residue contains at least 5carbon atoms. Examples of hydroxyl group-containing monomers which aresuitable as component (b) are, in particular, the reaction product of 1mol of hydroxyethyl acrylate and/or hydroxyethyl methacrylate with onaverage 2 mol of ε-caprolactone and/or the reaction product of acrylicacid and/or methacrylic acid with the glycidyl ester of a carboxylicacid having a tertiary α carbon atom. These glycidyl esters ofcarboxylic acids which have from 11 to 13 carbon atoms and are branchedon the α carbon atom (Versatic acid) are commercially available, forexample, under the name Cardura® from Shell. The reaction of the acrylicand/or methacrylic acid with the glycidyl ester can in this context becarried out before, during or after the polymerization.

However, as component (b) it is also possible to employ alkyl esters ofacrylic acid and/or methacrylic acid, for example hydroxypentylacrylates and methacrylates, hydroxyhexyl acrylates and methacrylates,hydroxyoctyl acrylates and methacrylates, etc., and/or hydroxylgroup-containing esters of a polymerizable ethylenically unsaturatedcarboxylic acid which are different from (a), for example the hydroxylgroup-containing esters of crotonic and isocrotonic acid.

As component (c) it is possible in principle to employ any aliphatic orcycloaliphatic esters of acrylic acid or of methacrylic acid which haveat least 4 carbon atoms in the alcohol residue and are different from(a) and (b), or a mixture of such monomers. Examples are: aliphaticesters of acrylic acid and of methacrylic acid, having 4 to 20 carbonatoms in the alcohol residue, for example n-butyl, isobutyl, tert-butyl,n-hexyl, 2-ethylhexyl, stearyl and lauryl acrylate and methacrylates,and cycloaliphatic esters of (meth)acrylic acid, for example furfuryl,cyclohexyl, isobornyl, and t-butylcyclohexyl acrylate and methacrylate.

The composition of component (c) is preferably chosen such that thepolymerization of component (c) alone produces a polymethacrylate resinhaving a glass transition temperature of from -30 to +100° C.,preferably from -10 to +90° C.

As component (d), aromatic vinyl hydrocarbons are employed, such asstyrene, α-alkylstyrenes such as α-methylstyrenes, chlorostyrenes, o-,m- and p-methyl-styrene, 2,5-dimethylstyrene, p-methoxystyrene,p-tert-butylstyrene, p-dimethylaminostyrene, p-acetamido styrene andvinyltoluene, with vinyltoluenes and, in particular, styrene beingpreferably employed.

As component (e) it is possible in principle to employ any ethylenicallyunsaturated carboxylic acid or a mixture of ethylenically unsaturatedcarboxylic acids. As component (e) it is preferred to employ acrylicacid and/or methacrylic acid.

As component (f) it is possible in principle to employ any ethylenicallyunsaturated monomer which is different from (a), (b), (c), (d) and (e),or a mixture of such monomers. Examples of monomers which can beemployed as component (f) are: amides of acrylic acid and methacrylicacid, for example methacrylamide and acrylamide; nitriles of methacrylicacid and acrylic acid; vinyl ethers and vinyl esters.

The composition of component (e) is preferably chosen such that thepolymerization of component (e) alone produces a polymer having a glasstransition temperature of from +70 to +185° C., preferably from +80 to+120° C.

It is also essential to the invention that the coating compositionsaccording to the invention contain as crosslinking agent (B) a mixturecomprising

(B1) at least one polymer of an aliphatic and/or cycloaliphatic and/orof an araliphatic di- and/or polyisocyanate having an averagefunctionality of from 3 to 4 and having a uretdione group content of notmore than 5%,

(B2) optionally at least one polymer of an aliphatic and/orcycloaliphatic and/or of an araliphatic di- and/or polyisocyanate havingan average functionality of from 2 to 3 and having a uretdione groupcontent of from 20 to 40%, and

(B3) optionally at least one aliphatic and/or cycloaliphatic and/oraraliphatic di- or poly isocyanate which is different from (B1) and(B2).

The coating compositions preferably contain as crosslinking agent (B) amixture comprising

(B1) from 40 to 100% by weight of component (B1),

(B2) from 0 to 60% by weight of component (B2), and

(B3) from 0 to 25% by weight of component (B3),

the sum of the proportions by weight of components (B1) to (B3) being ineach case 100% by weight and the proportions by weight being based ineach case on the solids content.

Furthermore, the composition of the curing component (B) is withparticular preference tailored to the composition of the acrylate resin(A):

If the acrylate resin (A) has been prepared using more than 14% byweight, based on the overall weight of the monomers (a) to (f) employed,of hydroxyl group-containing monomers which are different from (a1) (ie.monomers selected from the group consisting of hydroxypropylmethacrylate and/or hydroxypropyl acrylate and/or component (b)), thenthe mixture employed as component (B) preferably comprises

(B1) from 45 to 89% by weight of component (B1),

(B2) from 11 to 55% by weight of component (B2), and

(B3) from 0 to 10% by weight of component (B3).

If the acrylate resin (A) has been prepared using not more than 14% byweight, based on the overall weight of the monomers (a) to (f) employed,of hydroxyl group-containing monomers which are different from (a1) (ie.monomers selected from the group consisting of hydroxypropylmethacrylate and/or hydroxypropyl acrylate and/or component (b)), thenthe mixture employed as component (B) preferably comprises

(B1) from 45 to 100% by weight of component (B1),

(B2) from 0 to 55% by weight of component (B2), and

(B3) from 0 to 10% by weight of component (B3).

In the coating compositions according to the invention, it is preferredto employ as component (B1) and (B2) polymers based on3,5,5-trimethyl-1-isocyanato-3-isocyanatomethylcyclohexane and, inparticular, polymers based on hexamethylene diisocyanate.

Examples of isocyanate compounds which are suitable as component (B1)are the products which are available commercially under the followingnames:

Desmodur® N 3390 from Bayer AG, a 90% strength solution of a trimerbased on hexamethylene diisocyanate, having a number-average molecularweight of about 700, an average functionality of between 3 and 4 and auretdione content of not more than 5%;

Tolonate® HD T90 from Rhone Poulenc, a polymer based on hexamethylenediisocyanate, having an average functionality of between 3 and 4, auretdione group content of not more than 5.0% by weight and a solidscontent of 90%.

One example of an isocyanate compound which is suitable as component(B2) is the product which is commercially available under the followingname:

Desmodur® N 3400 from Bayer AG, a trimer based on hexamethylenediisocyanate, having a number-average molecular weight of about 500, anaverage functionality between 2 and 3 and a uretdione group content ofbetween 30 and 40%.

One example of an isocyanate compound which is suitable as component(B3) is the product which is commercially available under the followingname:

Desmodur® Z 4370 from Bayer AG, a 70% strength solution of apolyisocyanate based on an isophorone diisocyanate trimer, having anaverage functionality of from 2.9 to 3.7.

In addition, the following polyisocyanates may be employed as component(B3):

cycloaliphatic isocyanates, for example 1,3-cyclo pentane,1,4-cyclohexane, 1,2-cyclohexane and isophorone diisocyanate, aliphaticisocyanates such as trimethylene, tetramethylene, pentamethylene,hexamethylene and trimethylhexamethylene 1,6-diisocyanate, andtris-hexamethylene triisocyanate.

Preference is given to employing diisocyanates having isocyanate groupsof different reactivity, for example isophorone diisocyanate.

The quantity of the crosslinking agent employed is chosen such that theratio of the isocyanate groups of the crosslinking agent to the hydroxylgroups of component (A) is in the range from 1:3 to 3:1. The coatingcompositions according to the invention usually contain from 15 to 45%by weight of the acrylate resin (A) and from 6 to 20% by weight of thecrosslinking agent (B), based in each case on the overall weight of thecoating composition and based on the solids content of components (A)and (B).

The coating compositions according to the invention may additionallycontain, if desired, one or more other hydroxyl group-containing resins,whereby, for example, the solvent resistance and hardness of theresulting coating are improved further. For example, they may containfurther hydroxyl group-containing acrylate resins, which are differentfrom the above-described acrylate resin (A), and/or polycondensationresins (especially polyesters).

These further binders are usually employed in a quantity of from 0 to25% by weight, based in each case on the overall weight of the coatingcomposition and based on the solids content of the binder.

Examples of suitable additional binders are, for example, thepolyacrylate resins which are commercially available under the nameMacrynal® SM 510 and SM 513 from Hoechst, and the hydroxylgroup-containing polyacrylate resins which are described in GermanPatent Application DE-A-40 24 204 and are prepared in the presence of apolyester. For details reference is made to DE-A-40 24 204, especiallypage 3, line 18 to page 7, line 53.

Also suitable are hydroxyl group-containing polyacrylate resins whichare obtainable by polymerizing

(m₁) from 5 to 80% by weight, preferably from 5 to 30% by weight, of acycloaliphatic ester of methacrylic acid and/or acrylic acid, or of amixture of such monomers,

(m₂) from 10 to 50% by weight, preferably from 15 to 40% by weight, of ahydroxyl group-containing alkyl ester of methacrylic acid and/or acrylicacid, or of a mixture of such monomers,

(m₃) from 0 to 25% by weight, preferably from 0to 15% by weight, of ahydroxyl group-containing ethylenically unsaturated monomer which isdifferent from (m₁) and (m₂), or of a mixture of such monomers,

(m₄) from 5 to 80% by weight, preferably from 5 to 30% by weight, of analiphatic ester of methacrylic and/or acrylic acid, which is differentfrom (m₁), (m₂) and (m₃), or of a mixture of such monomers,

(m₅) from 0 to 40% by weight, preferably from 10 to 30% by weight, of anaromatic vinyl hydrocarbon which is different from (m₁), (m₂), (m₃) and(m₄), or of a mixture of such monomers, and

(m₆) from 0 to 40% by weight, preferably from 0 to 30% by weight, of afurther ethylenically unsaturated monomer which is different from (m₁),(m₂), (m₃), (m₄) and (m₅), or of a mixture of such monomers,

to give a polyacrylate resin having a number-average molecular weight Mnof from 1000 to 5000, a ratio of weight-average molecular weight Mw tonumber-average molecular weight Mn of less than 5.0, preferably from 1.8to 4.0, and an OH number of from 60 to 180, preferably from 100 to 150,mg of KOH/g, the sum of the proportions by weight of components (m₁) to(m₆) always being 100% by weight, and where, as component (m₂), onlymonomers or mixtures of monomers are employed which on polymerization ofthe particular monomer alone produce a polyacrylate and/orpolymethacrylate resin having a glass transition temperature of from-10° C. to +6° C. or from +60° C. to 80° C.

As component (m₂) it is preferred to employ 3-hydroxypropyl methacrylateand/or 2-hydroxypropyl methacrylate and/or 3-hydroxypropyl acrylateand/or 2-hydroxypropyl acrylate. Examples of the monomers which aresuitable as components (m₁) and (m₃) to (m₆) are the monomers describedin the course of the description of the acrylate resin (A) which isemployed in accordance with the invention.

The coating compositions according to the invention additionally containone or more organic solvents. These solvents are commonly employed inquantities of from 20 to 70% by weight, preferably from 25 to 65% byweight, based in each case on the overall weight of the coatingcomposition. Examples of suitable solvents are relatively highlysubstituted aromatic substances, for example solvent naphtha, heavybenzole, various Solvesso® grades, various Shellsol® grades and Deasol®,and relatively high-boiling aliphatic and cycloaliphatic hydrocarbons,for example various white spirits, mineral terpentine oil, tetralin anddecalin and various esters, for example ethylglycol acetate, butylglycolacetate, ethyldiglycol acetate and the like.

The coating compositions according to the invention may additionallycontain conventional auxiliaries and additives in conventionalquantities, preferably from 0.01 to 10% by weight based on the overallweight of the coating composition. Examples of suitable auxiliaries andadditives are leveling agents such as silicone oils, plasticizers suchas phosphates and phthalates, viscosity-controlling additives, mattingagents, UV absorbers, light stabilizers and, if desired, fillers.

The coating compositions are prepared in a known manner by mixing and,if desired, dispersing the individual components.

These coating compositions can be applied to a substrate in the form ofa film by spraying, flow coating, dipping, rolling, knife-coating orbrushing, the film subsequently being cured to give a firmly adheringcoating.

These coating compositions are commonly cured at room temperature orslightly elevated temperature, preferably at slightly elevatedtemperature, advantageously at temperatures of below 120° C., preferablyat temperatures below 80° C. and preferably at temperatures of about 60°C. However, the coating compositions may also be cured under bakingconditions, i.e. at temperatures of at least 120° C. In this case,however, it should be ensured that the crosslinking component does notcontain any polyisocyanates (B2).

Suitable substrates are, in particular, metals and also wood, plastic,glass and the like.

Owing to the short curing times and low curing temperatures, the coatingcompositions according to the invention are preferably used forautomotive refinishing, the finishing of large vehicles and goodsvehicle bodies. However, depending on the crosslinking agent employed,they can also be utilized for the production-line finishing of motorvehicles. Furthermore, they are particularly suitable as a clearcoat.

The present invention therefore also relates to a process for producinga multicoat protective and/or decorative finish on a substrate surface,in which

(1) a pigmented basecoat is applied to the substrate surface,

(2) a polymer film is formed from the basecoat applied in step (1),

(3) a transparent topcoat containing

(A) a hydroxyl group-containing polyacrylate resin and

(B) a crosslinking agent is applied to the resulting basecoat, andsubsequently

(4) basecoat and topcoat are cured together, characterized in that thetopcoat employed is the coating composition according to the invention.

The basecoats employed in this process are known and therefore requireno further description. Examples of suitable basecoats include thebasecoats described in DE-A 41 10 520, DE-A 40 09 000, DE-A 40 24 204,EP-A-355433, DE-A 35 45 618, DE-A 38 13 866 and in German PatentApplication P 42 32 717.2, which is not a prior publication.

Also suitable are the basecoats described in German Patent Application P43 27 416.1, which has not yet been published, which are characterizedin that they contain a hydroxyl group-containing polyester having aweight-average molecular weight Mw of 40,000-200,000 and apolydispersity Mw/Mn>8, and in that at least 50% by weight of aromaticdicarboxylic acids or esterifiable derivatives thereof have beenemployed for the preparation of the polyester, but where the content ofphthalic anhydride is not more than 80% by weight and the percentages byweight are based in each case on the overall weight of the acidcomponents employed in the preparation of the polyester.

The coating compositions according to the invention can also be used forapplication over oxidatively drying, pigmented oxidatively drying andpigmented 2-component polyurethane coating materials which areconventionally employed in the sector of optionally one-coat automotiverefinishing. In this case too, coatings having the desired advantageousproperties are obtained.

The coating compositions according to the invention are particularlynotable for good adhesion to the basecoat, good mar resistance and ahigh degree of hardness of the resulting coatings. In addition, thecoating compositions exhibit rapid drying coupled with prolongedprocessability (long pot life). In addition, the resulting coatings,especially in the case of clearcoats, display good mechanical propertiessuch as, for example, good gloss retention, good fullness, good levelingand a good topcoat appearance.

The invention is now illustrated in more detail with reference toembodiment examples. All parts and percentages in these examples are byweight unless expressly stated otherwise.

I. Preparation of the Hydroxyl Group-containing Acrylate Resins E1 to E4and V1 to V2

The monomers employed for the preparation of the hydroxylgroup-containing acrylate resins are compiled in Table 1. Thenumber-average and weight-average molecular weights were determined byGPC measurements against a polystyrene standard. The hydroxy-n-propylmethacrylate employed represented a commercial mixture of 25% by weightof 3-hydroxy-n-propyl methacrylate and 75% by weight of2-hydroxy-n-propyl methacrylate. The properties of the resultingacrylate resins are shown in Table 2.

I.1. Preparation of the Hydroxyl Group-containing Acrylate Resin E1

1164 g of Solventnaphtha® (aromatic solvent mixture having a boilingrange of from 160 to 185° C.) were initially introduced into a 4lreactor which is suitable for polymerization reactions, and were heatedunder nitrogen with stirring at 140° C. A monomer mixture of 180 g ofstyrene, 1121.4 g of butyl methacrylate, 180 g of hydroxypropylmethacrylate, 280.8 g of 4-hydroxybutyl acrylate and 31.8 g of acrylicacid was metered over the course of 4 h, and a mixture of 108 g oftert-butyl peroxyethylhexanoate and 108 g of Solventnaphtha® over aperiod of 4.75 h, into this initial charge, at a uniform rate andbeginning simultaneously. After the end of the initiator feed, the batchwas after polymerized for 2 h. The finished polyacrylate resin has asolids content of 57.6% (130° C. 1 h), an acid number of 17.3 and anoriginal viscosity of 7.0 dPa.s (Mn=2192; Mw=5740).

I.2. Preparation of the Hydroxyl Group-containing Acrylate Resin E2

1164 g of Solventnaphtha® were initially introduced into a 4 1 reactorwhich is suitable for polymerization reactions, and were heated undernitrogen with stirring at 140° C. A monomer mixture of 180 g of styrene,1121.4 g of butyl methacrylate, 360 g of hydroxypropyl methacrylate,100.8 g of 4-hydroxybutyl acrylate and 37.8 g of acrylic acid wasmetered over the course of 4 h, and a mixture of 108 g of tert-butylperoxyethylhexanoate and 108 g of Solventnaphtha® over a period of 4.75h, into this initial charge, at a uniform rate and beginningsimultaneously. After the end of the initiator feed, the batch was afterpolymerized for 2 h. The finished polyacrylate resin has a solidscontent of 57.6% (130° C. 1 h), an acid number of 17.6 and an originalviscosit849 y of 12.8 dPa.s (Mn=2166; Mw=6115).

I.3. Preparation of the Hydroxyl Group-containing Acrylate Resin E3

1164 g of Solventnaphtha® were initially introduced into a 1 l reactorwhich is suitable for polymerization reactions, and were heated undernitrogen with stirring at 140° C. A monomer mixture of 180 g of styrene,1121.4 g of butyl methacrylate, 270 g of hydroxypropyl methacrylate, 191g of 4-hydroxybutyl acrylate and 37.8 g of acrylic acid was metered overthe course of 4 h, and a mixture of 108 g of tert-butylperoxyethylhexanoate and 108 g of Solventnaphtha® over a period of 4.75h, into this initial charge, at a uniform rate and beginningsimultaneously. After the end of the initiator feed, the batch was afterpolymerized for 2 h. The finished polyacrylate resin has a solidscontent of 57.6% (130° C. 1 h), an acid number of 17.6 and an originalviscosity of 7.8 dPa.s (Mn=2150; Mw=5900).

I.4 Preparation of the Hydroxyl Group-containing Acrylate Resin V1

1003 g of Solventnaphtha® were initially introduced into a 1 l reactorwhich is suitable for polymerization reactions, and were heated undernitrogen with stirring at 140° C. A monomer mixture of 180 g of styrene,1121.4 g of butyl methacrylate, 460.8 g of hydroxypropyl acrylate, and37.8 g of acrylic acid was metered over the course of 4 h, and a mixtureof 108 g of tert-butyl peroxyethylhexanoate and 108 g of Solventnaphtha®over a period of 4.75 h, into this initial charge, at a uniform rate andbeginning simultaneously. After the end of the initiator feed, the batchwas after polymerized for 2 h. The finished polyacrylate resin has asolids content of 59.1% (130° C. 1 h), an acid number of 16.5 and anoriginal viscosity of 6.6 dPa.s (Mn=2241; Mw=7211).

I.5 Preparation of the Hydroxyl Group-containing Acrylate Resin V2

1358 g of Solventnaphtha® were initially introduced into a 4l reactorwhich is suitable for polymerization reactions, and were heated undernitrogen with stirring at 140° C. A monomer mixture of 210 g of styrene,1308 g of butyl methacrylate, 538 g of hydroxypropyl methacrylate, and44 g of acrylic acid was metered over the course of 4 h, and a mixtureof 126 g of tert-butyl peroxyethylhexanoate and 126 g of Solventnaphtha®over a period of 4.75 h, into this initial charge, at a uniform rate andbeginning simultaneously. After the end of the initiator feed, the batchwas after-polymerized for 2 h. The finished polyacrylate resin has asolids content of 56.2% (130° C. 1 h), an acid number of 18.7 and anoriginal viscosity of 22.5 dPa.s (Mn=2346; Mw=8856).

I.6. Preparation of the Hydroxyl Group-containing Acrylate Resin E4

1164 g of Solventnaphtha® were initially introduced into a 4l reactorwhich is suitable for polymerization reactions, and were heated undernitrogen with stirring at 140° C. A monomer mixture of 180 g oftert-butylcyclohexyl acrylate, 1121 g of butyl methacrylate, 360 g ofhydroxypropyl methacrylate, 101 g of hydroxy-butyl acrylate and 38 g ofacrylic acid was metered over the course of 4 h, and a mixture of 108 gof tert-butyl peroxyethylhexanoate and 108 g of Solventnaphtha® over aperiod of 4.75 h, into this initial charge, at a uniform rate andbeginning simultaneously. After the end of the initiator feed, the batchwas after-polymerized for 2 h. The finished polyacrylate resin has asolids content of 56.3% (130° C. 1 h), an acid number of 17.6 and anoriginal viscosity of 5.3 dPa.s (Mn=1909; Mw=4963).

II. Preparation of the Coating Compositions E1 to E4 and V1 to V2(Comparison Examples)

II.1. Preparation of the Curing Solutions 1 to 4

The curing solutions are prepared from the components indicated below bymixing:

    ______________________________________                                        Curing agent  E1     E2        E3   E4                                        ______________________________________                                        Butyl acetate 98%                                                                           49.0   49.0      49.0 44.5                                        Butylglycol acetate 6.0 6.0 6.0 6.0                                           Catalyst solution.sup.1) 1.5 1.5 1.5 1.5                                      Desmodur ® N 3400.sup.2) 19.5 10.0 5.0 --                                 Desmodur ® N 3390.sup.3) 24.0 33.5 38.5 48                                Solids content (%) 41 40 40 44                                              ______________________________________                                         .sup.1) Catalyst solution described in section II.3.                          .sup.2) Commercial waterthinnable polyisocyanate from Bayer AG based on a     hexamethylene diisocyanate dimer/trimer, having a numberaverage molecular     weight of about 500, an average functionality of between 2 and 3 and a        uretdione group content of between 30 and 40%.                                .sup.3) Commercial polyisocyanate from Bayer AG, a 90% strength solution      in 1:1 butyl acetate/solvent naphtha of a trimer based on hexamethylene       diisocyanate, having a numberaverage molecular weight of about 700, an        average functionality of between 3 and 4 and a uretdione group content of     not more than 5%.                                                        

II.2. Preparation of an Adjustment Additive

An adjustment additive is prepared from the components indicated belowby mixing:

    ______________________________________                                        xylene           20.0                                                           Solvent naphta ®  15.0                                                    Benzine 135/180 10.0                                                          Butylglycol acetate 5.0                                                       Butyl acetate 50.0                                                          ______________________________________                                    

II.3. Preparation of a Catalyst Solution

1.0 part of dibutyltin dilaurate is mixed with 99.0 parts of butylacetate 98/100.

II.4. Preparation of a Leveling Agent Solution

5.0 parts of a commercial leveling agent based on a polyether-modifiedmethylpolysiloxane (commercial product Baysilone OL 44 from Bayer AG)and 95.0 parts of xylene are mixed.

II.5. Preparation of the Clearcoat Solutions E1 to E4 and V1 to V2

The clearcoat solutions are prepared from the components indicated inTable 3 by mixing.

II.6. Preparation of the Transparent Topcoats E1 to E4 and V1 to V2(Comparison Examples)

The transparent topcoats are prepared by mixing in each case 100 partsby volume of the clearcoat solutions E1 to E4 or V1 to V2, respectively,with 50 parts by volume of the above-described curing solutions E1 to E4and 30 parts by volume of the above-described adjustment additive. Thecomposition of the topcoats is shown in Tables 4 to 8.

The coating material obtained in this way is then applied tophosphatized and coated steel panels. To this end the phosphatized steelpanels are coated with a commercial conventional filler (commercialproduct Glasurit Grundfuller [primer surfacer] 801-1552 from GlasuritGmbH, Munster) with a binder based on an epoxide group-containing binderand with an amino-functional curing agent, dried at 80° C. for 20 minand at room temperature for 24 h and then coated with a commercialconventional metallic basecoat (commercial product Basislack [basecoat]54 A 926 from Glasurit GmbH, Munster) based on a hydroxylgroup-containing polyester, cellulose acetobutyrate, wax and a melamineresin. After a flash-off time of 30 min the clearcoat is applied. Thepanels are then dried at 60° C. for 30 min and at room temperature for16 h.

The results from the testing of the resulting coatings are given inTables 4 to 8.

                  TABLE 1                                                         ______________________________________                                        Composition of the acrylate resins in % by weight                                            E1     V1     V2   E2   E3   E4                                ______________________________________                                        Styrene        10     10     10   10   10   --                                  t-Butylcyclohexyl acrylate -- -- -- -- -- 10                                  n-Butyl methacrylate 62.3 62.3 62.3 62.3 62.3 62.3                            4-Hydroxy-n-butyl acrylate 15.6 25.6 -- 5.6 10.6 15.6                         3-Hydroxy-n-propyl 10.0 -- 25.6 20.0 15.0 10                                  methacrylate                                                                  Acrylic acid  2.1  2.1  2.1  2.1  2.1  2.1                                  ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Properties of the acrylate resins                                                      E1      V1      V2    E2    E3    E4                                 ______________________________________                                        OH number                                                                              100     100     100   100   100   100                                  [mg of KOH/g]                                                                 Acid number 17.3 16.5 18.7 17.6 17.6 17.6                                     [mg of KOH/g]                                                                 M.sub.n 2192 2241 2346 2166 2150 1909                                         M.sub.w 5740 7211 8856 6115 5900 4963                                         M.sub.n /M.sub.w 2.6 3.2 3.8 2.8 2.7 2.6                                      Tg (° C.) +13.6 -1.3 +40.5 +30.3 +21.7 +28.4                           Tg (c) (° C.) 20 20 20 20 20 +26.0                                     Tg (a) (° C.) -26.6 -65 +73 +29.1 -1.6 +29.1                           η [dpas.s] 7.0 6.6 22.5 12.8 7.8 5.3                                      SC [%] 57.6 59.1 56.2 57.6 56.6 56.3                                        ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        Composition of the clearcoat solutions in parts by weight                                  V1      V2     E1   E2    E3   E4                                ______________________________________                                        Acrylate V1.sup.1)                                                                         90.-    --     --   --    --   --                                  Acrylate V2.sup.1) -- 90.- -- -- -- --                                        Acrylate E1.sup.1) -- -- 90.- -- -- --                                        Acrylate E2.sup.1) -- -- -- 90.- -- --                                        Acrylate E3.sup.1) -- -- -- -- 90.- --                                        Acrylate E4.sup.1) -- -- -- -- -- 90.-                                        Tinuvin 292.sup.2)  0.9  0.9  0.9  0.9  0.9  0.9                              Tinuvin 1130.sup.3)  0.9  0.9  0.9  0.9  0.9  0.9                             DBTL solution.sup.4)  2.0  2.0  2.0  2.0  2.0  2.0                            Leveling agent solution.sup.5)  3.8  3.8  3.8  3.8  3.8  3.8                  Butylglycol acetate  2.4  2.4  2.4  2.4  2.4  2.4                             Solids content 55% 52% 54% 54% 53% 53%                                      ______________________________________                                         Explanations for Table 3                                                      .sup.1) acrylate resin solutions described under section I.1 to I.6.          .sup.2) commercial light stabilizer from Ciba Geigy based on a sterically     hindered amine (HALS)                                                         .sup.3) commercial light stabilizer from Ciba Geigy based on benzotriazol     .sup.4) catalyst solution described under section II.3.                       .sup.5) leveling agent solution described under section II.4.            

                  TABLE 4                                                         ______________________________________                                        Composition of the coating compositions based on the clearcoat                  solution E1 and properties of the resulting coatings                            Example        1      2       3     4                                     ______________________________________                                        Clearcoat solution E1                                                                        100    100       100   100                                       Adjustinent additive 30 30 30 30                                            Curing agent.sup.1)                                                                      E1      50     --      --    --                                       E2 -- 50 -- --                                                                E3 -- -- 50 --                                                                E4 -- -- -- 50                                                             Viscosity [s].sup.2)                                                                         15     15        16    17                                        Viscosity after 2 h [s].sup.2) 17 17 18 19                                    Mar test.sup.3) <1  7  8 24                                                   Crosshatch.sup.4) Gt2 Gt2 Gt2 Gt2                                             Hardness.sup.5) 3B 3B-2B 3B-2B 3B-2B                                          Volvo test.sup.6) ml/gl ml/gl ml/gl ml/gl                                     Topcoat appearance.sup.7) satisf. satisf. satisf. satisf.                   ______________________________________                                    

                  TABLE 5                                                         ______________________________________                                        Composition of the coating compositions based on the clearcoat                  solution E2 and properties of the resulting coatings                            Example        5       6      7     8                                     ______________________________________                                        Clearcoat solution E2                                                                        100     100      100   100                                       Adjustinent additive 30 30 30 30                                            Curing agent.sup.1)                                                                      E1      50      --     --    --                                       E2 -- 50 -- --                                                                E3 -- -- 50 --                                                                E4 -- -- -- 50                                                             Viscosity [s].sup.2)                                                                         15      15       16    17                                        Viscosity after 2 h [s].sup.2) 17 17 18 19                                    Mar test.sup.3)  5  8 18 24                                                   Crosshatch.sup.4) Gt1 Gt1-2 Gt1-2 Gt1                                         Hardness.sup.5) 2B-3B 2B 2B 2B-B                                              Volvo test.sup.6) ml/gl ml/gl ml/gl ml/gl                                     Topcoat appearance.sup.7) satisf. satisf. satisf. satisf.                   ______________________________________                                    

                  TABLE 6                                                         ______________________________________                                        Composition of the coating compositions based on the clearcoat                  solution E3 and properties of the resulting coatings                            Example        9       10     11    12                                    ______________________________________                                        Clearcoat solution E3                                                                        100     100      100   100                                       Adjustment additive 30 30 30 30                                             Curing agent.sup.1)                                                                      E1      50      --     --    --                                       E2 -- 50 -- --                                                                E3 -- -- 50 --                                                                E4 -- -- -- 50                                                             Viscosity [s].sup.2)                                                                         15      15       16    17                                        Viscosity after 2 h [s].sup.2) 17 17 18 19                                    Mar test.sup.3)  1  8 13 28                                                   Crosshatch.sup.4) Gt1-2 Gt1-2 Gt1-2 Gt1                                       Hardness.sup.5) 2B-3B 2B 2B 2B-B                                              Volvo test.sup.6) ml/gl ml/gl ml/gl ml/gl                                     Topcoat appearance.sup.7) satisf. satisf. satisf. satisf.                   ______________________________________                                    

                  TABLE 7                                                         ______________________________________                                        Composition of the coating compositions based on the clearcoat                  solution E4 and properties of the resulting coatings                            Example        13      14     15    16                                    ______________________________________                                        Clearcoat solution E4                                                                        100     100      100   100                                       Adjustment additive 30 30 30 30                                             Curing agent.sup.1)                                                                      E1      50      --     --    --                                       E2 -- 50 -- --                                                                E3 -- -- 50 --                                                                E4 -- -- -- 50                                                             Viscosity [s].sup.2)                                                                         14      14       15    16                                        Viscosity after 2 h [s].sup.2) 15 15 17 17                                    Mar test.sup.3)  3  3  4  6                                                   Crosshatch.sup.4) Gt1 Gt1 Gt1 Gt1                                             Hardness.sup.5) 2B-3B 2B-3B 2B-3B 2B-B-3B                                     Volvo test.sup.6) ml/gl ml/gl ml/gl ml/gl                                     Topcoat appearance.sup.7) satisf. satisf. satisf. satisf.                   ______________________________________                                    

                                      TABLE 8                                     __________________________________________________________________________    Composition of the coating compositions based on the clearcoat solution       V1 and                                                                          V2 and properties of the resulting coatings                                 Example   V1 V2  V3 V4 V5  V6  V7  V8                                         __________________________________________________________________________    Clearcoat solution V1                                                                   100                                                                              100 100                                                                              100                                                                              --  --  --  --                                           Clearcoat solution V2 -- -- -- -- 100  100  100  100                          Adjustment additive 30 30 30 30 30 30 30 30                                 Curing agent.sup.1)                                                                  E1 50 --  -- -- 50  --  --  --                                            E2 -- 50 -- -- -- 50 -- --                                                    E3 -- -- 50 -- -- -- 50 --                                                    E4 -- -- -- 50 -- -- -- 50                                                 Viscosity [s].sup.2)                                                                    15 15  16 17 14  15  15  17                                           Viscosity after 2 h [s].sup.2) 18 19 20 23 17 17 18 19                        Mar test.sup.3) <1 <1 <1 <1 78 80 83 84                                       Crosshatch.sup.4) Gt5 Gt5 Gt5 Gt5 Gt0-1 Gt1 Gt1 Gt0-1                         Hardness.sup.5) >3B >3B >3B >3B B HB-B HB-B HB-B                              Volvo test.sup.6) ml/gl ml/gl ml/gl ml/gl ml/gl ml/gl ml/gl ml/gl                                               Topcoat appearance.sup.7) satisf.                                            satisf. satisf. satisf. satisf.                                               satisf. satisf. satisf.                    __________________________________________________________________________

Explanations for Table 4 to 8

The tests indicated in Tables 4 to 8 are carried out as follows:

1) curing solutions described under section II.1.

2) viscosity, measured as flow time from the DIN 4 cup directly and 2 hafter preparation of the coating composition

3) The mar resistance was determined using a steel cylinder weighing 2 gwhich is provided on the bottom face with a 2 cm thick rubber diskhaving a diameter of 4.5 cm, which is covered in turn on the bottom facewith a nylon fabric having a mesh size of about 30 μm. The cylinder isplaced vertically on the coated panel to be tested. The overallconstruction is connected via a rod, just above the rubber disk, to aneccentric disk which is driven by a motor. The size of the disk ischosen such that a path of about 10-15 cm in length is produced parallelto the surface of the test panel.

Procedure:

Testing is carried out using the coated steel panels described above,having a size of about 10×20 cm. The test panel is wetted with about 0.5ml of an aqueous solution which contains surfactant. The test cylinderis then mounted. 80 double strokes are made over the surface within aperiod of about 80 s. Subsequently, after 1 h, the DL value is measuredvertically to the direction of movement of the cylinder under an angleof observation of 20° with respect to the surface (DL value measured inaccordance with DIN 6174, standard light source D, 3 angle measuringinstrument MMK111 from Datacolor).

4) The crosshatch was determined by applying a 1 mm long crosscut to thecleaned, grease-free test panel, using the automatic crosshatchinstrument model 430 from Erichsen GmbH, Hemer-Sundwig, Germany. The cutsite is cleaned using a brush. A wooden spatula is used to press onTesaband® 4651 adhesive tape, which is then removed with a yank.

The evaluation is carried out in accordance with DIN 53151.

5) The pencil hardness was determined using pencils from Faber Castell,Germany.

The pencil points are ground flat for this test, using P400 sandpaper,in an angle of about 90°. Marks about 5 cm long are then made on thecoated surface, by hand, at an angle of 45°. This is done using apressure such that the pencil point just fails to break.

Evaluation: a record is made of the grade of pencil with which nofurther marking can be seen on the coated surface.

6) Volvo crack test:

Test conditions 1 cycle:

4 h at 50° C. in an oven

2 h at 35° C. and 95-100% rel. atmospheric humidity

2 h at 35° C. and 95-100% rel. atmospheric humidity and 2 l of sulfurdioxide

16 h at -30° C. in a deep-freeze cabinet

Wash panel with water and dry

Evaluation:

Degree of blistering in accordance with DIN 53209

Cracks ASTM D660

Summary of the Test Results

Although the coatings of Comparison Examples 1 to 4 are of good marresistance, the adhesion (crosshatch test) and the hardness arecompletely inadequate.

Although the coatings of Comparison Examples 5 to 8 show a good adhesionto the basecoat (crosshatch test) and good hardness, the mar resistanceof the resulting coatings is completely inadequate. The mar resistanceis also not improved by variation of the curing agents.

The comparison of Examples 1 to 12 with the Comparison Examples 1 to 8shows that, by using a mixture of hydroxypropyl methacrylate andhydroxybutyl acrylate as monomer component, the adhesion to the basecoatand the hardness of the resulting coating is distinctly improved incomparison with the use of hydroxybutyl acrylate as the sole monomercomponent. At the same time however, despite the use of hydroxypropylmethacrylate, the mar resistance of the resulting coatings is at leastadequate (Examples 4, 8 and 12) and can be further improved by anappropriate choice for the composition of the curing solution (good tovery good mar resistance in Examples 1 to 3, 5 to 7 and 9 to 11).Furthermore, Examples 1 to 12 show that, although the mar resistancedecreases as the proportion of hydroxypropyl methacrylate rises (but atthe same time, however, the hardness and adhesion increase), thisreduction in mar resistance can be compensated, at least partially,however, by an increased proportion of the curing component (B2).

What is claimed is:
 1. A coating composition comprising a binderconsisting of(A) a hydroxyl group containing polyacrylate resin, and (B)at least one crosslinking agent, wherein1.) component (A) consists ofthe reaction product obtained by polymerizing(a) from 10 to 51% byweight of a mixture comprising(a1) one or more monomers selected fromthe group consisting of 4-hydroxy-n-butyl acrylate, 4-hydroxy-n-butylmethacrylate, 3-hydroxy-n-butyl acrylate, 3-hydroxy-n-butylmethacrylate, and (a2) one or more monomers selected from the groupconsisting of 3-hydroxy-n-propyl acrylate, 3-hydroxy-n-propylmethacrylate, 2-hydroxy-n-propyl acrylate, 2-hydroxy-n-propylmethacrylate, (b) from 0 to 20% by weight of one or more monomersselected from the group consisting of hydroxyl group-containing estersof acrylic acid or of methacrylic acid which are different from (a) andhave at least 5 carbon atoms in the alcohol residue and hydroxylgroup-containing esters of polymerizable ethylenically unsaturatedcarboxylic acids, which are different from (a), (c) from 28 to 85% byweight of an aliphatic or cycloaliphatic ester of acrylic acid or ofmethacrylic acid which is different from (a) and (b) and has at least 4carbon atoms in the alcohol residue, or of a mixture of such monomers,(d) from 0 to 25% by weight of an aromatic vinyl hydrocarbon which isdifferent from (a), (b) and (c), or a mixture of such monomers, (e) from0 to 5% by weight of an ethylenically unsaturated carboxylic acid, or ofa mixture of ethylenically unsaturated carboxylic acids, and (f) from 0to 20% by weight of an ethylenically unsaturated monomer which isdifferent from (a), (b), (c), (d) and (e), or of a mixture of suchmonomers, to give a polyacrylate resin having a hydroxyl number of from60 to 200 mg of KOH/g, an acid number of from 0 to 35 mg of KOH/g and anumber average molecular weight of from 1000 to 5000, the sum of theproportions by weight of components (a) to (f) being in each case 100%by weight, and further wherein(2.) component (B) is a mixturecomprising(B 1) at least one polymer selected from the group consistingof aliphatic, cycloaliphatic, and araliphatic di- and polyisocyanateshaving an average functionality of from 3 to 4 and having a uretdionegroup content of not more than 5%, (B2) optionally, at least one memberselected from the group consisting of polymers of aliphatic,cycloaliphatic, and araliphatic di and polyisocyanates having an averagefunctionality of from 2 to 3 and having a uretedione group content offrom 20 to 40%, and (B3) optionally, at least one aliphatic,cycloaliphatic, or araliphatic di- or polyisocyanate.
 2. A coatingcomposition according to claim 1, wherein the hydroxyl group-containingpolyacrylate resin is obtained by polymerizing(a) from 10 to 35% byweight of component (a), (b) from 0 to 10% by weight of component (b),(c) from 40 to 70% by weight of component (c), (d) from 5 to 20% byweight of component (d), (e) from 1 to 3% by weight of component (e),and (f) from 0 to 15% by weight of component (f).
 3. A coatingcomposition according to claim 1, wherein the composition of component(a) is selected such that the polymerization of component (a) aloneproduces a polyacrylate resin having a glass transition temperature offrom -62 to +65° C.
 4. A coating composition according to claim 1,wherein the mixture employed as component (a) comprisesfrom 10 to 85% byweight of component (a1) and from 15 to 90% by weight of component(a2),the sum of the proportions by weight of components (a1) and (a2)being in each case 100% by weight.
 5. A coating composition according toclaim 1, wherein the mixture employed as component (a) comprises(a1) atleast one of 4-hydroxy-n-butyl acrylate or 3-hydroxy-n-butyl acrylate,and (a2) at least one of 3-hydroxy-n-propyl methacrylate or2-hydroxy-n-propyl methacrylate.
 6. A coating composition according toclaim 1, wherein the composition of component (c) is selected such thatthe polymerization of component (c) alone produces a polyacrylate resinhaving a glass transition temperature of from -30 to 100° C.
 7. Acoating composition according to claim 1, wherein component (c) isselected from the group consisting of n-butyl (meth)acrylate, isobutyl(meth)acrylate, tert-butyl (meth)acrylate, furfuryl (meth)acrylate,n-hexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate,cyclohexyl (meth)acrylate and tert-butylcyclohexyl (meth)acrylate.
 8. Acoating composition according to claim 1, wherein the polyacrylate resinhas a number-average molecular weight from 1800 to 3500, a hydroxylnumber of from 80 to 160 mg of KOH/g and an acid number of from 0 to 25mg of KOH/g.
 9. A coating composition according to claim 1, wherein thecrosslinking agent (B) is a mixture offrom 40 to 100% by weight ofcomponent (B1), from 0 to 60% by weight of component (B2), and from 0 to25% by weight of component (B3),the sum of the proportions by weight ofcomponents (B1) to (B3) being in each case 100% by weight and theproportions by weight being based in each case on the solids content.10. A coating composition according to claim 9, wherein the crosslinkingagent (B) is a mixture offrom 45 to 89% by weight of component (B1),from 11 to 55% by weight of component (B2), and from 0 to 10% by weightof component (B3); with the proviso that the acrylate resin (A) has beenprepared using more than 14% by weight, based on the overall weight ofthe monomers (a) to (f) employed, of hydroxyl group-containing monomerswhich are different from (a1).
 11. A coating composition according toclaim 9, wherein at least one of components (B1) or (B2) is a polymer ofa member of the group consisting of3,5,5-trimethyl-1-isocyanato-3-isocyanatomethyl cyclohexane diisocyanateand hexamethylene diisocyanate.
 12. A process for producing a multicoatprotective and/or decorative finish on a substrate surface, comprisingthe steps of:(1) applying a pigmented basecoat to the substrate surface,(2) forming a polymer film from the basecoat applied in step (1), (3)applying a transparent topcoat composition according to claim 1 to theresulting basecoat, and subsequently (4) curing basecoat and topcoattogether.
 13. The process according to claim 12, wherein an automotiverefinish topcoat is produced.
 14. A coating composition according toclaim 1, wherein the composition of component (a) is selected such thatthe polymerization of component (a) alone produces a polyacrylate resinhaving a glass transition temperature of from -50 to +35° C.
 15. Acoating composition according to claim 1, wherein the mixture employedas component (a) comprises from 20 to 65% by weight of component (a1)and from 35 to 80% by weight of component (a2), the sum of theproportions by weight of components (a1) and (a2) being in each case100% by weight.
 16. A coating composition according to claim 1, whereinthe composition of component (c) is selected such that thepolymerization of component (c) alone produces a polyacrylate resinhaving a glass transition temperature of from -10 to +90° C.
 17. Acoating composition according to claim 9, wherein the crosslinking agent(B) is a mixture of from 45 to 100% by weight of component (B1), from 0to 55% by weight of component (B2), and from 0 to 10% by weight ofcomponent (B3); with the proviso that the acrylate resin (A) has beenprepared using not more than 14% by weight, based on the overall weightof the monomers (a) to (f) employed, of hydroxyl group-containingmonomers which are different from (a1).